Field of the Invention
Disclosed features relate to a technique for an image processing apparatus to correct an image deformation caused by an atmospheric fluctuation or the like.
Description of the Related Art
When a moving image is captured with a video camera, a monitoring camera, or the like, the captured video image may fluctuate due to an influence of an atmospheric fluctuation. The video image fluctuation is a phenomenon that occurs as a result of random refraction of light beams due to a non-uniform atmospheric temperature distribution and a non-uniform atmospheric density distribution, and changes therein. The video image fluctuation leads to an irregular deformation of the shape of a subject in the captured video image both spatially and temporally from the normal shape of the subject. Such a fluctuation phenomenon is a cause for decrease in the visibility of the video image. The fluctuation phenomenon also is a cause for erroneous detection in a monitoring camera system that automatically detects a predetermined subject. Thus, the fluctuation is desired to be corrected.
Japanese Patent Application Laid-Open No. 2012-182625 discusses, as a technique for correcting a fluctuation in a video image, a method in which a mean filter or a median filter of a plurality of time-series frames is applied to respective pixel values of pixels in a video image. When deformation of a subject occurs as a result of the aforementioned video image fluctuation, respective points on the subject are moved randomly in the video image. Destinations of the moved points are considered to have a distribution centered on positions where those points are supposed to appear. Thus, a pixel located at a position where a point of interest is supposed to appear is likely to have a pixel value of the point of interest. As such, the technique discussed in Japanese Patent Application Laid-Open No. 2012-182625 employs time-series filtering processing to acquire an image with no fluctuation.
Further, Japanese Patent Application Laid-Open No. 03-095686 discusses a method in which a fluctuation in a video image is extracted as a motion vector between images, the extracted motion vector is traced to obtain a center of the fluctuation, and a pixel that is an origin of the fluctuation is rearranged at the center position. In this way, a normal position where a point is supposed to appear is estimated. According to the technique discussed in Japanese Patent Application Laid-Open No. 03-095686, the fluctuation is corrected by transforming the shape of a subject in such a manner that respective points in the video image are moved toward the obtained normal positions of the points.
However, in a case where a video image (a plurality of pieces of image data captured sequentially in time series) includes a moving subject, the fluctuation correction techniques discussed in Japanese Patent Application Laid-Open Nos. 2012-182625 and 03-095686 cause a deterioration in image quality of a region where the moving subject exists (also referred to as “moving region”).